Apparatuses using laser light as a light source of a projection type projector, which is used for a movie or home theater, have been developed. In such a laser light source which serves as a light source, it is known that there are a case where light emitted directly from a semiconductor laser element is used, and a case where the wavelength of light emitted from the semiconductor laser element is converted to wavelength different therefrom by a nonlinear optical crystal in order to use the light. In recent years, laser light sources have been developed as blue or green laser light sources in which Periodically Poled Lithium Niobate (PPLN: Periodically Poled Lithium Niobate), or Periodically Poled Lithium Tantalate (PPLT: Periodically Poled Lithium Tantalate), etc. is used for such a nonlinear optical crystal. For example, what is disclosed in Patent Literature Document 1 is known as such technology. The Patent Documents 1 discloses that a laser light source apparatus comprises a light source, which is made up of a semiconductor laser; a wavelength conversion element (which is a nonlinear optical crystal, for example, PPLN) which receives and converts laser light emitted from the light source, into second harmonics; and an external resonator which chooses light of predetermined wavelength emitted from the wavelength conversion element, and which reflects it toward the light source (for example, volume bragg grating: VBG: Volume Bragg Grating). Moreover, it discloses that a temperature adjusting unit is provided between the wavelength conversion element and a subbase to which the wavelength conversion element is attached. Furthermore, it discloses that since an interval of a polarization reversal cycle of a wavelength conversion element can be adjusted by adjusting the temperature of the wavelength conversion element using the temperature adjusting unit, it becomes possible to improve the light conversion efficiency.
FIG. 16 is a block diagram showing one form of a conventional laser light source apparatus, and explanation of the prior art in which the temperature of a wavelength conversion element is set as the optimal temperature, will be given referring to the figure. A wavelength conversion element 5 (for example, PPLN) mounted on a laser light source unit LH has a function to perform wavelength conversion for converting the wavelength of light emitted from the laser light source element 2 (which, is, for example, a semiconductor laser, and which will be referred to as a semiconductor laser) into wavelength shorter than that of the incidence light, and for example, infrared rays can be converted into green light. In addition, there is the optimal temperature of the wavelength conversion element 5 (for example, PPLN) at which the optical conversion efficiency can be maximized. Moreover, as for this optimal temperature, there is a variation depending on individual pieces, and if the temperature shifts from the optimal point by 0.5 degrees Celsius, the conversion efficiency will get worse by 10% or more. Light, which is not converted, is consumed as heat as it is. Then, in general, optimal temperature conditions of the wavelength conversion element are looked for, and if the optimal temperature conditions are found, the temperature of the wavelength conversion element 5 is detected by a temperature detection unit Th1, whereby control is performed so that the temperature of the wavelength conversion element 5 may become the optimal temperature by controlling a heating unit, for example, the heater 7, for heating the wavelength conversion element 5 from the outside, by a temperature adjusting unit.
In order to find the optimal control temperature of the wavelength conversion element 5, conventionally, for example, a method described below has been used. While driving the laser light source unit LH by a laser light source lighting apparatus 100 and sweeping control temperature of the wavelength conversion element 5 in an assumed temperature range, as shown in FIG. 16, for example, a light output measuring apparatus 110 such as a photo cell or an optical power meter, is used to measure light output emitted from the laser light source unit. And the control temperature, which is the maximum in light output when the sweeping measurement is completed, is saved, and this value is adopted as the optimal control temperature, whereby the temperature of the wavelength conversion element is controlled so as to become the optimal control temperature. However, in this method, a unit for measuring light output is needed so that there is a problem that unnecessary cost incurs.
A block diagram of another configuration example of a conventional laser light source apparatus is shown in FIG. 17. This example is a configuration example in case where a laser is in series connected. As shown in FIG. 17, for the purpose of the cost cut of the laser light source apparatus, a method of connecting, in series, two or more semiconductor lasers 2 to each other in one laser light source lighting apparatus 100 is known widely. In this form, because a switching element, a control circuit, etc. in the laser light source lighting apparatus 100 can be shared, a lighting power source can be cheaply supplied. Moreover, it is configured so that three lights outputted from respective laser light source units LH1-LH3 are condensed by using an optical element PZs such as prisms, thereby emitting light. As described above, when the two or more laser elements are used, adjustment of the optimal temperature of each wavelength conversion element 5 is individually needed, so that there is a problem that it takes a lot of time to perform the adjustments. That is, in measurement in which a photo cell shown in FIG. 16 is used, only one laser light source unit LH is measured and the optimal temperature of the laser light source unit which is subject thereto is adjusted. However, as shown in the figure, when the laser light source units LH1-LH3 are in series connected, it is impossible to stop only one laser since the same current flows through the three lasers, so that it is difficult to adjust the optimal temperature of the wavelength conversion element 5.